In-band signaling for data communications over digital wireless telecommunications networks

ABSTRACT

An inband signaling modem communicates digital data over a voice channel of a wireless telecommunications network. An input receives digital data. An encoder converts the digital data into audio tones that synthesize frequency characteristics of human speech. The digital data is also encoded to prevent voice encoding circuitry in the telecommunications network from corrupting the synthesized audio tones representing the digital data. An output then outputs the synthesized audio tones to a voice channel of a digital wireless telecommunications network.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/133,186 filed Apr. 26, 2002, which is a divisional of U.S.application Ser. No. 09/602,593 filed Jun. 22, 2000 and now U.S. Pat.No. 6,493,338, which is a CIP of U.S. application Ser. No. 09/531,367filed Mar. 21, 2000 and now U.S. Pat. No. 6,690,681, which is a CIP ofU.S. application Ser. No. 09/230,079 filed May 13, 1999 and now U.S.Pat. No. 6,144,336, which is the U.S. national phase applicationcorresponding to International Application No. PCT/US98/10317 filed May19, 1998.

TECHNICAL FIELD

This disclosure relates to wireless telecommunications and morespecifically to a system that transmits digital data over the audiochannel of a digital wireless network “in-band.”

BACKGROUND

A cellular telephone allows a user to talk to another user without beingtethered to a “land line.” The cell phone includes circuitry thatsamples the audio signals from the user's voice. These voice signals areconverted into a digital form using an A-D converter. The digitizedvoice signals are encoded by a voice coder (vocoder) and then modulatedonto a carrier frequency that transmits the voice signals over a cellnetwork. The voice signals are sent over the wireless cellular networkeither to another phone in the wireless cell network or to another phonein a land-line phone network.

Different coders/decoders (codecs), modulators, vocoders, Automatic GainControllers (AGC), Analog to Digital converters (A/D), noise reductioncircuits, and Digital to Analog converters (D/A) are used in thecellular and landline phone networks. These telephone components canimplement different coding schemes for encoding and decoding the voicesignals.

These telecommunication components are designed to efficiently transmitvoice signals over wireless and landline voice communication channels.For example, a digital vocoder uses predictive coding techniques torepresent the voice signals. These predictive coders filter out noise(non-voice signals) while compressing and estimating the frequencycomponents of the voice signals before being transmitted over the voicechannel.

A problem arises when voice communication equipment, such as thevocoder, are used for transmitting digital data. The vocoders mayinterpret signals representing digital data as a non-voice signal. Thevocoder might completely filter out or corrupt those digital datasignals. Therefore, digital data can not be reliably transmitted overthe same digital audio channel used for transmitting voice signals.

It is sometimes necessary for a user to transmit both audio signals anddigital data to another location at the same time. For example, when acellular telephone user calls “911” for emergency assistance, the usermay need to send digital location data to a call center while at thesame time verbally explaining the emergency conditions to a humanoperator. It would be desirable to transmit this digital data through acell phone without having to use a separate analog wireless modem.

Accordingly, a need exists for transmitting digital data over a voicechannel of a digital wireless communications network.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a wireless communications network thatprovides in-band signaling (IBS) according to one embodiment.

FIG. 2 a detailed diagram of a cellular telephone coupled to an IBSmodem according to one embodiment.

FIG. 3 is another embodiment of the IBS modem.

FIG. 4 is a detailed diagram of an IBS modem encoder.

FIG. 5 is a schematic diagram of a IBS packet.

FIG. 6 is a schematic diagram of digital data tones output from a IBSmodulator.

FIG. 7 is a diagram showing how digital data is corrupted by anAutomatic Gain Controller.

FIG. 8 is a diagram showing how a digital wireless network can filterout digital data tones.

FIG. 9 is a detailed diagram of receiving circuitry coupled to an IBSmodem decoder.

FIG. 10 is a state diagram for the IBS decoder shown in FIG. 9.

FIG. 11 is a block diagram showing a search state in the IBS decoder.

FIG. 12 is a block diagram showing an active state in the IBS decoder.

FIG. 13 is a block diagram showing a clock recovery state in the IBSdecoder.

FIG. 14 is a schematic diagram of a cellular phone with the IBS modemlocated in a detachable battery pack.

FIG. 15 are schematic diagram showing different data sources coupled toa cellular telephone through a IBS modem.

FIG. 16 is a schematic diagram showing implementation of the IBS modemusing a sound card.

FIGS. 17 and 18 are block diagrams showing how the sound card in FIG. 16operates.

FIG. 19 is a block diagram of a synchronization circuit for the IBSmodem.

FIG. 20 is a detailed diagram of the synchronization circuit in FIG. 19.

FIG. 21 is a timing diagram showing how the synchronization circuit inFIG. 19 operates.

FIG. 22 is a graph showing how the synchronization circuit identifiesthe optimum synchronization start time.

FIG. 23 is an alternative implementation of the synchronization circuit.

FIG. 24 is an encoder diagram for a multichannel IBS modem.

FIG. 25 is an decoder diagram for a multichannel IBS modem.

FIGS. 26 and 27 show different channel configurations for themultichannel IBS modem shown in FIGS. 24 and 25.

FIG. 28 is an encoder diagram for a multicarrier IBS modem.

FIG. 29 is an decoder diagram for a multicarrier IBS modem.

DETAILED DESCRIPTION

With reference to the above-listed drawings, this section describesparticular embodiments and their detailed construction and operation.The embodiments described herein are set forth by way of illustrationonly. Those skilled in the art will recognize in light of the teachingsherein that variations can be made to the embodiments described hereinand that other embodiments are possible. No attempt is made toexhaustively catalog all possible embodiments and all possiblevariations of the described embodiments.

For the sake of clarity and conciseness, certain aspects of componentsor steps of certain embodiments are presented without undue detail wheresuch detail would be apparent to those skilled in the art in light ofthe teachings herein and/or where such detail would obfuscate anunderstanding of more pertinent aspects of the embodiments.

According to one embodiment, an inband signaling modem communicatesdigital data over a voice channel in a digital wirelesstelecommunications network. An input receives digital data. An encoderconverts the digital data into audio tones that synthesize frequencycharacteristics of human speech. The digital data is also encoded toprevent voice encoding circuitry in the telecommunications network fromcorrupting the synthesized audio tones representing the digital data. Anoutput then outputs the synthesized audio tones to a voice channel of adigital wireless telecommunications network.

Referring to FIG. 1, a wireless communications network 12 includes acell phone 14 that receives voice signals 22 from a user 23. A voicecoder (vocoder) 18 in the cell phone 14 encodes the voice signals 22into encoded digital voice signals 31 that are then transmitted over awireless digital radio channel 34 (cell call). The cell phone 14transmits the encoded voice signals 31 to a cellular communications site(cell site) 36 that relays the cell call to a CellularTelecommunications Switching System (CTSS) 38.

The CTSS 38 either connects the cell call to another cell phone eitherin the wireless cellular network 12, to a landline phone on a PSTNnetwork 42 as a circuit switched call or routes the cell call over apacket switched Internet Protocol (IP) network 46 as a Voice Over IP(VoIP) call. The cell call can also be routed from the PSTN network 42back to the cellular network 12 or from the PSTN network 42 to the IPnetwork 46, or visa versa. The cell call eventually reaches a telephone44 that corresponds with a destination phone number originally enteredat the cell phone 14.

Additional data could be inserted at any point in the cellular network12, such as in PSTN network 42 and IP network 46 and the signalremodulated for transmission over wireline or cellular networks. Suchdata could be system related such as routing information, toll or tariffinformation, etc.

An In-Band Signaling (IBS) modem 28 enables cell phone 14 to transmitdigital data 29 from a data source 30 over the radio channel 34 of thecellular network 12. The IBS modem 28 modulates the digital data 29 intosynthesized digital data tones 26. The digital data tones 26 prevent theencoding components in the cellular network 12 and landline network 42,such as vocoder 18, from corrupting the digital data. The encoding andmodulation scheme used in the IBS modem 28 allows digital data 29 to betransmitted through the same voice coder 18 used in the cell phone 14for encoding voice signals 22. Any appliance such as a vending machine,etc could be enhanced by this technology.

Synthesized tones are defined as signals that represent digital datathat also have signaling characteristics that enable the signals to beencoded and decoded by a voice codec without losing the digital datainformation in the signal. In one example, Frequency Shift Keying (FSK)signals are used to created the synthesized tones at differentfrequencies within the audio range of human speech.

The IBS modem 28 enables voice signals 22 and digital data 29 to betransmitted over the same digital audio channel using the same cellphone circuitry. This prevents a user from having to transmit digitaldata using a separate wireless modem and enables a cell phone user totalk and send data during the same digital wireless call.

According to one embodiment, the digital data 29 is modulated intosynthesized audio tones. This prevents the cell phone vocoder 18 fromfiltering or corrupting the binary values associated with the digitaldata 29. The same cell phone transceiver and encoding circuitry is usedfor transmitting and receiving both voice signals and digital data. Thisenables the IBS modem 28 to be much smaller, less complex and moreenergy efficient than a standalone wireless modem. In some embodiments,the IBS modem 28 is implemented entirely in software using only theexisting hardware components in the cell phone 14.

One or more servers 40 are located at any of various locations in thewireless network 12, PSTN network 42, or IP network 46. Each server 40includes one or more IBS modems 28 that encode, detect and decode thedigital data 29 transmitted and received over the digital radio channel34. Decoded digital data is either processed at the server 40 or routedto another computer, such as computer 50.

Referring to FIG. 2, a first transmitting portion of the IBS modem 28includes an IBS encoder 52 and a Digital to Analog converter (D/A) 54.The IBS encoder 52 is typically implemented using a Digital SignalProcessor (DSP). The data source 30 represents any device that requireswireless transmission or reception of digital data. For example, thedata source 30 can be a laptop computer, a palm computer or a GlobalPositioning System (GPS) (see FIG. 15).

The data source 30 outputs a digital bit stream 29 to the IBS encoder52. The IBS encoder 52 converts the digital data 29 into IBS packetsspecially formatted for transmission over a digital wireless voicechannel. The IBS encoder 52 then converts the bits from the IBS packetsinto digital data tones that are then fed into the D/A converter 54.

The IBS modem 28 outputs binary values that each represent an amplitudeand phase component of an audio tone. The D/A converter 54 convertsthese digital values into analog audio tones 26 that are then output toan auxiliary audio port 15 on the cell phone 14. The analog audio tones26 are then processed by the cell phone 14. An Analog to Digital (A/D)converter 16 in the cell phone 14 encodes the synthesized analog audiotones 26 into digital values. The vocoder 18 encodes the digitalrepresentations of the synthesized tones 26 into encoded digital data 32and outputs the encoded data to a transceiver 19 that transmits theencoded digital data 32 over the radio channel 34.

The preferred voltage of the synthesized audio tones 26 output from theD/A converter 26 is around 25 millivolts peak to peak. This voltagelevel was discovered to prevent the audio tones 26 from saturating thevoice channel circuitry in cell phone 14.

Because the digital data 29 is fed through the existing auxiliary handsfree audio port 15 in cell phone 14, the IBS modem 28 can be installedas an after market device that can connect any data source 30 to thecell phone 14. The data source 30 can transmit digital data 29 in anydigital format. For example, the digital data 29 can be sent over anRS-232 interface, Universal Serial Bus (USB) interface, or any otherserial or parallel interface.

FIG. 3 shows an alternative embodiment of the IBS modem 28. The IBSmodem 28 in FIG. 3 is located inside the cell phone 14 and isimplemented in software using the existing cell phone processor or usingsome combination of its own components and the existing cell phonecomponents. In this embodiment, the cell phone 14 may include a dataport 56 that receives the digital data 29 from the external data source30. In an alternative embodiment, the digital data source 30 is internalto the cell phone 14. For example, the data source 30 may be a GlobalPositioning System (GPS) chip that includes a GPS receiver (not shown)for receiving global positioning data from GPS satellites (FIG. 14).

The IBS encoder 52 in FIG. 3 as mentioned above is typically implementedin software using a DSP and may use the same DSP used for implementingthe vocoder 18. The D/A converter 54 outputs the synthesized audio tonesrepresenting digital data 29 to the internal A/D converter 16 of thecell phone 14. The IBS encoder 52 in an alternative embodiment, not onlysynthesizes the digital data 29 into audio tones but also quantizes thedigital frequency values. The IBS encoder 52 then outputs the quantizeddata 55 directly into the vocoder 18. In still another embodiment, theIBS encoder 52 is implemented entirely in software in the same DSP thatimplements the vocoder 18

The vocoder 18 uses a specific encoding scheme associated with thewireless communications network 12 (FIG. 1). For example, the vocoder 18could be a VCELP encoder that converts voice signals into digital CDMAsignals. The A/D converter 16, D/A converter 54 and transceiver 19 areexisting cell phone components known to those skilled in the art.

It is important to note that the IBS encoder 52 enables the digital data29 to be transmitted using the same cell phone circuitry that transmitsvoice signals. The IBS encoder 52 prevents any signal approximation,quantization, encoding, modulation, etc. performed by the, A/D converter16, vocoder 18, or transceiver 19 from corrupting or filtering any bitsfrom the digital data 29.

FIG. 4 is a detailed diagram of the IBS encoder 52 shown in FIG. 2 andFIG. 3. A data buffer 58 stores the binary bit stream 29 from the datasource 30. A packetizer 60 segments the bits in buffer 58 into bytesthat comprise a IBS packet payload. A packet formatter 62 adds a packetpreamble and postamble that helps prevent corruption of the IBS packetpayload. An IBS modulator 64 then modulates the bits in the IBS packetwith two or more different frequencies 66 and 68 to generate digitaldata tones 69.

Preventing Corruption of Digital Data in Voice Channels

Cell phone voice coders increase bandwidth in voice channels by usingpredictive coding techniques that attempt to describe voice signalswithout having to send all the information associated with human speech.If any unnatural frequencies or tones are generated in the voice channel(i.e., frequencies representing digital data), those frequencies mightbe thrown out by the voice coder 18 (FIG. 2). For example, if theamplitude of the digital data tones are greater than that of normalvoice signals or the same digital data tone is generated for too long atime period, the voice coder 18 might filter out that high amplitude orextended frequency signal. Depending on how the digital data tones areencoded, the digital bits represented by those unnatural audio tones maybe partially or entirely removed from the voice channel.

The IBS encoder 52 encodes the digital data 29 in a manner where voicecoders will not filter or corrupt the tones representing digital data.The IBS encoder 52 does this by controlling the amplitudes, time periodsand patterns of the synthesized audio tones used to represent the binarybit values.

Referring to FIG. 5, the packet formatter 62 (FIG. 4) adds a packetpreamble 73 and a header 75 to the front of a IBS packet 70. The packetpreamble 73 includes a preamble pattern 72 and a sync pattern 74. Achecksum 78 and a packet postamble 79 are attached to the backend of theIBS packet 70.

FIG. 6 shows the synthesized digital data tones 69 output from the IBSmodulator 64 (FIG. 4). The IBS modulator 64 (FIG. 4) converts thedigital bits in the IBS packet 70 into one of two different tones. Afirst tone is generated at an f1 frequency and represents a binary “1”value and a second tone is generated at a f2 frequency and represents abinary “0” value. In one embodiment the f1 frequency is 600 Hertz andthe f2 frequency is 500 Hertz (Hz).

It has been determined that the most effective frequency range forgenerating the tones that represent the binary bit values are somewherebetween 400 Hertz and 1600 Hertz. The IBS modulator 64 includes Sine andCosine tables that are used to generate the digital values thatrepresent the different amplitude and phase values for the f1 and f2frequencies.

In one embodiment, the digital data is output on the radio channel 34 ata baud rate of 100 bits/second. This baud rate has been found to beeffective in preventing corruption of the digital audio data by a widevariety of different cellular telephone voice coders. The sine waves foreach f1 and f2 tone begin and end at a zero amplitude point and continuefor a duration of 10 milliseconds. Eighty samples are generated for eachdigital data tone.

Referring to FIG. 7, an Automatic Gain Controller (AGC) 80 is oneencoding function used in the cell phone 14. The AGC 80 may be softwarethat is located in the same DSP that implements the voice coder 18. TheAGC 80 scales instantaneous energy changes in voice signals. There aresituations when no voice signals have been fed into the AGC 80 for aperiod of time followed by a series of audio tones 82 that comprise thebeginning of a IBS packet 70. The AGC 80 scales the first group of tones82 at the beginning of the IBS packet 70. The AGC 80 also looks ahead atthe zero signal levels 84 after the end of the IBS packet 70, and willscale the tones 83 at the end of the IBS packet 70 as part of itsprediction scaling scheme. This scaling prevents the over amplificationof signal or noise when instantaneous energy changes occur in the voicechannel.

As previously shown in FIG. 6, the “1” and “0” bits of the IBS packet 70are represented by tones f1 and f2, respectively. If these tones arescaled by the AGC 80, the digital bits represented by those frequenciesmight be dropped during encoding. For example, the vocoder 18 may seethe scaled tones as noise and filter them from the audio channel. Toprevent the unintentional filtering of tones that represent digitaldata, the IBS packet 70 in FIG. 5 includes preamble bits 72 andpostamble bits 79. The preamble bits 72 and postamble bits 79 do notcontain any of the digital data bits 29 from the data source but includea certain number of sacrificial bit(s) that are not needed for detectingor encoding the IBS packet 70. The tones that are generated for thesesacrificial bits in the preamble and postamble can be scaled or filteredby the AGC 80 without effecting any of the digital data contained in theIBS packet payload 76.

The bit pattern in the preamble 72 and sync pattern 74 are specificallyformatted to further prevent corruption of the packet payload 76. Arandom sequence and/or an alternating “1”-“0” sequence of bits is usedin either the preamble 72 and/or sync pattern 74. These alternating orrandom bit patterns prevent adaptive filters in the cell phone vocoder18 (FIG. 2) from filtering tones representing the remaining bits in theIBS packet 70.

Referring to FIG. 8, adaptive filters adapt around the frequencies thatare currently being transmitted over the wireless network. For example,if a long period of the same f1 tone is currently being transmitted, anadaptive filter used in the cell phone may adapt around that f1frequency spectrum as shown by filter 86.

Another short tone at another frequency f2 may immediately follow thelong period of f1 tones. If the filter 86 is too slow to adapt, thefirst few f2 tones may be filtered from the voice channel. If thefiltered f2 tone represent bits in the IBS bit stream, those bits arelost.

To prevent adaptive filters in the cell phone from dropping bits, someportion of the preamble 73 includes a random or alternating “1”-“0” bitpattern. This preconditions the adaptive filter as shown by filter 88.The preamble 73 (FIG. 5) tries to include a portion of the same bitsequence that is likely or does occur in the packet payload 76. Forexample, the IBS encoder 52 can look ahead at the bit pattern in thepayload 76. The encoder 52 can then place a subset of bits in a portionof the preamble to represent the sequence of bits in the packet payload.

This preconditions the adaptive filter for the same f1 and f2frequencies, in the same duration and in a similar sequence that islikely to follow in the IBS packet payload 76. Thus, the adaptive filteris less likely to filter out the tones that actually represent thedigital data that is being transmitted.

FIG. 9 is a block diagram of receive circuitry 91 that receives thevoice and data signals in the radio channel 34. The IBS modem 28 alsoincludes an IBS decoder 98 the detects and decodes the digital datatones transmitted in the radio channel 34. The receive circuitry 91 islocated at the CTSS 38 (FIG. 1) that receives wireless transmissionsfrom the cell sites 36 (FIG. 1). The same receive circuitry 91 is alsolocated in the cell phone 14.

As described above in FIGS. 2 and 3, the decoder part of the IBS modem28 can be external to the cell phone 14 or can be inside the cell phone14. Dashed line 104 shows an IBS modem 28 external to a cell phone anddashed line 106 shows an internal IBS modem 28 internal to a cell phone.IBS modems 14 can be located at any telephone location in the PSTNnetwork 42 or IP network 46 (FIG. 1). The receiving circuitry 91 may bedifferent when the IBS modem 28 is coupled to a landline. However, theIBS modem 28 operates under the same principle by transmitting andreceiving synthesized tones over the voice channel of the phone line.

The signals in radio channel 34 are received by a transceiver 90. Avocoder 92 decodes the received signals. For example, the vocoder 92 maydecode signals transmitted in TDMA, CDMA, AMPS, etc. A D/A converter 94then converts the digital voice signals into analog signals. The analogvoice signals are then output from an audio speaker 17.

If the IBS modem 28 is external to the receiving circuitry 91, then aA/D converter 96 converts the analog signals back into digital signals.The IBS decoder 98 demodulates any tones representing digital data backinto a digital IBS packets. A packet disassembler 100 disassembles thepacket payload from the IBS packets 70 and stores the decoded digitaldata in a data buffer 102.

FIG. 10 is a state diagram explaining how the IBS decoder 98 in FIG. 9operates. The IBS decoder 98 repeatedly samples and decodes the audiosignals received from the radio channel 34. State 110 searches for tonesin the audio signal that represent digital data. If the Signal to NoiseRatio (SNR), for tones within the frequency range of the digital datatones, are greater than a preselected value, the IBS decoder 98 goesinto an active state 112. The active state 112 collects tone samples. Ifat any time during the active state 112 the SNR falls below an activethreshold value or a timeout is reached before enough tone samples arecollected, the IBS decoder 98 returns to the search state 110 and beginsagain to search for digital data tones.

After a number of samples are collected, the IBS decoder 98 looks forbits that identify the preamble 73 in the IBS packet 70 (FIG. 5). If thepreamble 73 is detected, the IBS decoder 98 moves to clock recoverystate 114. The clock recovery state 114 synchronizes with thesynchronization pattern 74 in the IBS packet 70 (FIG. 5). The IBSdecoder 98 then demodulates the packet payload 76 in state 116. If thepreamble 73 is not found, IBS decoder 98 goes back to the search state110 and starts searching again for the beginning of an IBS packet 70.

The IBS decoder 98 demodulates all of the packet payload 76 and thenperforms a checksum 78 as a final verification that a valid IBS packet70 has been successfully demodulated. Control then returns back to thesearch state 110 and begins searching for the next IBS packet 70.

FIG. 11 is a detailed diagram for the search state 110 of the IBSdecoder 98. The search state 110 uses in band and out of band filtering.“In band” is used in the following discussion to refer to tones withinthe frequency range of the two tones that represent the digital databinary “1” value (500 Hz) and the digital data binary “0” value (600Hz).

A first band pass filter 118 (in band) measures energy for signals inthe audio channel within the frequency range of about 400 Hz to around700 Hz. A second band pass filter 120 (out of band) measures the energyin the audio channel for signals outside of the 400 Hz-700 Hz range. ASignal to Noise Ratio (SNR) is calculated in block 122 between the inband energy and the out of band energy. If tones representing thedigital data exist in the audio channel, the energy measured by the inband filter 118 will be much greater then the energy measured by the outof band filter 120.

If the SNR is below a selected threshold in comparator box 124, signalsin the audio channel are determined to be actual voice signals or noise.If the SNR is above the threshold, the IBS decoder 98 determines thetones represent in band digital data. When digital data is detected, theIBS decoder 98 moves into the active state 112 (FIG. 10) to beginsearching for the beginning of an IBS packet 70.

FIG. 12 shows the active state 112 for the IBS decoder 98. Block 130 isnotified by the search state 110 when an in band tone is detected in theaudio channel. Samples of the audio tones are windowed in block 132 witha number of samples associated with a single binary bit. In oneembodiment, 80 samples of the digital data tone are taken, padded withzeros, and then correlated with Discrete Fourier Transforms (DFTs).

A first DFT has coefficients representing a 500 Hz tone and is appliedto the windowed data in block 134. The first DFT generates a highcorrelation value if the samples contain a 500 Hz tone (“0” binary bitvalue). A second DFT represents a 600 Hz tone and is applied to thewindowed samples in block 136. The second DFT generates a highcorrelation value if the windowed samples contain a 600 Hz tone (“1”binary bit value). Block 138 selects either a binary “0” or binary “1”bit value for the windowed data depending on which of the 500 Hz DFT or600 Hz DFT yields the largest correlation value.

The IBS decoder 98 in decision block 140 continues to demodulate thetones until the preamble of the IBS packet 70 has been detected. The IBSdecoder 98 then moves to clock recovery state 114 (FIG. 13) tosynchronize with the sync pattern 74 in the IBS packet 70 (FIG. 5). Ifmore bits need to be demodulated before the preamble 73 can be verified,decision block 140 returns to block 132 and the next 80 samples of thedigital data tones are windowed and demodulated.

FIG. 13 describes the clock recovery state 114 for the IBS decoder 98.After the preamble 73 in the IBS packet 70 is detected in the activestate 112, the clock recovery state 114 demodulates the next string ofbits associated with the sync pattern 74 (FIG. 5). The clock recoverystate 114 aligns the tone samples with the center of the correlationfilters described in the active state 112. This improves decoderaccuracy when demodulating the IBS packet payload 76.

Decision block 142 looks for the sync pattern 74 in the IBS packet 70.If after demodulating the next tone, the sync pattern 74 is not found,decision block 142 offsets the window used for sampling the sync pattern74 by one sample in block 148. Decision block 150 then rechecks for thesync pattern 74. If the sync pattern 74 is found, decision block 144determines the power ratio for the detected sync pattern. This powerratio represents a confidence factor of how well the demodulator issynchronized with the sync pattern. The power ratio is compared with thepower ratios derived for different window shifted sampling positions. Ifthe power ratio is greater then a previous sampling position, then thatpower ratio is saved as the new maximum power ratio in block 146.

If the power ratio for the sync pattern 74 is less then the previouslymeasured power ratio, the decoder in block 148 offsets the samplingwindow by one sample position. The power ratio is then determined forthe shifted window and then compared to the current maximum power ratioin decision block 144. The window is shifted until the maximum powerratio is found for the sync pattern 74. The window offset value at themaximum power ratio is used to align the demodulator correlation filterswith the center sample of the first bit 77 (FIG. 5) in the IBS packetheader 75.

The IBS decoder 89 then jumps to demodulate state 116 (FIG. 10) wherethe identified window offset is used to demodulate the remaining 500 and600 Hz tones that represent the packet payload bits 76 and check sumbits 78. The demodulation state 116 correlates the f1 and f2 tones withDFTs in the same manner as in the active state (FIG. 12). The check sumbits 78 are then used as a final check to verify that a valid IBS packethas been received and accurately decoded.

FIG. 14 is a diagram of the IBS modem 28 located in a battery packconnected to the cellular telephone 14. A hands free audio channel pin200 couples the IBS modem 28 to the voice channel 202 in the cell phone14. A switch 204 couples either voice signals from the microphone 17 ordigital data tones from the IBS modem 28 to the voice channel 202.

The switch 204 is controlled either through a menu on a screen (notshown) in the cell phone 14 or by a button 206 that extends out of theback end of the battery pack 208. The switch 204 can also be controlledby one of the keys on the keyboard of the cell phone 14.

The button 206 can also be used to initiate other functions providedthrough the IBS modem 28. For example, a Global Positioning System (GPS)includes a GPS receiver 210 located in the battery pack 208. The GPSreceiver 210 receives GPS data from a GPS satellite 212. A cell phoneoperator simply pushes button 206 during an emergency situation.Pressing the button 206 automatically enables the GPS receiver 210 tocollect GPS data from GPS satellite 212. At the same time, the switch204 connects IBS modem 28 on the voice channel 202 of the cell phone 14.The IBS modem 28 is then activated. As soon as the GPS data is collectedin the IBS modem 28, the data is formatted, encoded and output by IBSmodem 28 to the voice channel 202 of the cell phone 14.

The user 23 can push the button 206 anytime after manually calling up aphone number. After the audio channel is established with anotherendpoint, the user 23 pushes button 206. Switch 204 is connected to theIBS modem 28 and the IBS modem 28 is activated. The GPS data (or otherdigital source) is then sent as digital data tones through the IBS modem28 to an endpoint over the established audio channel. After the data hasbeen successfully transmitted, the user presses button 206 againreconnecting switch 204 to the audio receiver 17.

FIG. 15 shows the different types of data sources that can be connectedto the IBS modem 28. Any one of a palm computer 212, GPS receiver 214 ora computer 216, etc. can are coupled to the IBS modem 28. The IBS modem28 converts the bits output from the device into digital data tones thatare then output over the radio channel 34 in the wireless network.Because data can be transmitted to another endpoint through the cellphone 14, none of the devices 212, 214 or 216 need a separate wirelessmodem.

Implementation of Inband Signaling Modem in a Sound Card

The IBS modem can be implemented in a standard computer sound card.Referring to FIG. 16, a sound card 252, such as a Sound Blaster cardmanufactured by Creative Labs, Inc., 1523 Cimarron Plaza; Stillwater,Okla. 74075 is included in a computer 250. A speaker output 253 of thesound card 252 outputs audio tones to a hands free port 257 on a cellphone 258. A microphone input 259 on the sound card 252 is connected tothe speaker output of the cell phone 258.

The computer includes a processor 254 that converts digital data into anaudio format used by the sound card 252 to output synthesized audiotones. The cell phone 258 encodes and transmits those audio tones overthe voice channel of a wireless communications network. A cell site 261receives the transmitted audio tones and forwards the audio tones over aPSTN network 263. A computer 262 is connected to a telephone line 260 atthe destination location of the phone call. Another sound card 264 and aprocessor 266 in computer 262 demodulate the audio tones back intodigital data. The digital data represented by the audio tones aredisplayed on computer 262. The sound cards may be used for dataencoding, decoding or both. The sound cards may be used at computer 250,computer 262, or both.

Referring to FIGS. 16 and 17, data files, GPS data, data entered by thekeyboard by a user, or any other digital data is packetized andformatted by computer 250 into IBS packets in block 270. Packetizationand packet formatting is described in FIGS. 4 and 5. The binary bitvalues in the IBS packets are converted in block 272 into a digitalformat used by the sound card 252 (FIG. 16) for generating synthesizedaudio tones. For example, binary “1” bit values in the IBS packet areconverted into a digital format representing a first f1 frequency toneand binary “0” bit values are converted into a second f2 frequency tone.The f1 and f2 tones are generated similar to the manner described inFIG. 6.

The sound card in block 274 outputs analog tones representing the binarybit values in a manner similar to the IBS encoder 52 and the digital toanalog converter 54 described in FIG. 3. The cell phone in block 276encodes the audio tones and transmits the encoded audio tones over thevoice channel in the wireless communications network in block 278.

Referring to FIGS. 16 and 18, the cellular phone call is establishedwith a destination phone number. In block 280, either a user picks upthe ringing phone line or the computer 262 (FIG. 16) at the destinationend of the cellular phone call is programmed to detect a ringing signalfrom the telephone line 260. If a ring signal is detected, either a useror the computer 262 in block 282 generates an “hook-off” signal on thetelephone line 260. The sound card 264 in block 284 acts like an analogto digital converter by converting the audio tones on the telephone line260 into digital data. The sound card 264 in conjunction with theprocessor 266 (FIG. 16) decodes the IBS audio tones similar to the IBSdecoder 98 described in FIGS. 9-13. The digital representations ofdetected IBS tones are then displayed on the screen of computer 262 inblock 290.

In one example, a user wants to find the location for cell phone 258.The user directs computer 262 (FIG. 16) to dial the phone number forcell phone 258. The computer 262 uses the sound card 264 to send IBStones that direct cell phone 258 to send back GPS location data. Thecomputer 250 may have a GPS receiver or the cell phone 258 may have astandalone GPS receiver. If the GPS receiver and the IBS modem areinternal to the cell phone 258 as shown in FIGS. 2-9, the computer 250does not need to be connected to the cell phone 258.

The GPS data is converted into IBS tones either by the sound card 252 asdescribed in FIG. 17 or through an internal IBS modem as described inFIGS. 2-9. The IBS tones representing the GPS data are transmitted backover the wireless telecommunications channel and the PSTN network 263 tothe telephone line 260. The sound card 264 in computer 262 monitors thephone line 260 for the IBS audio tones. When detected, the IBS tones areconverted back into digital GPS data and displayed by processor 266 tothe user on the screen of computer 262. A mapping process in thecomputer 262 may then convert the GPS longitude and latitude values intoa state, city and street address.

Synchronization

FIG. 19 shows an alternative technique for demodulating andsynchronizing the IBS modem in the IBS decoder 300. The IBS audio tonesare received over the voice channel of the wireless communicationsnetwork at interface 301. The received tones are converted from analogto digital form by A/D converter 302. The IBS signal detector 304detects the presence of the IBS audio tones in the same manner asdescribed in FIG. 11.

The alternative synchronization technique begins with the decoder 300tuning the IBS signals to complex basebands with multipliers 306 and308. Multiplier 306 effectively moves any IBS tones at the first andsecond IBS frequencies f1 and f2 to DC. This first baseband signal isreferred to as S_(A)′ and the second baseband signal is referred to asS_(B)′. A matched filter bank 310 applies matched filters to thebaseband signals having the expected pulse shapes for the two audiotones representing the binary “1” and binary “0” values. The S_(A)signal output from the matched filter bank 310 represents a binary 1value and the S_(B) signal represents a binary 0 value. The matchedfilter bank can also add filtering to account for known characteristicsof the wireless communications channel that may exist in the S_(A) orS_(B) signals.

The matched filter is selected to match the pulse shaping applied to themodulator. The pulse shaping is selected for the best trade-off betweensignaling bandwidth, bit rate and inter symbol interference. The pulseshaping filter is applied to the integrated phase of the modulator'snumerical oscillator.

An IBS synchronizer 312 aligns the modulator with the synchronizationpattern attached to the front of the IBS packet. Segments 316 of samplesfrom the S_(A) and S_(B) signals are input to synchronizationdemodulator 314 along with a sample start time T_(B). The demodulator314 outputs a power value 320 to the IBS synchronizer 312 that indicateshow closely the demodulator is synchronized with the beginning bit inthe synchronization pattern. The IBS synchronizer 312 uses the powervalues 320 for each sample start time TB to determine the optimumsynchronization start time (*T_(B)) for demodulating the remaining bitsin the IBS packet. IBS packet modulator 322 then uses the optimum starttime *T_(B) to demodulate the binary bit values from the S_(A) and S_(B)signals.

FIG. 20 is a more detailed description of the sync demodulator 314 andthe IBS packet demodulator 322 in FIG. 19. A first integrator 324integrates the first segment of samples for the S_(A) signal. Theintegrator starts at sample start time T_(B) and integrates N number ofsamples representing the duration T of one IBS bit (Baud time). Arectifier 326 feeds the magnitude of the integration value into an adder332. In a similar matter, an integrator 328 integrates the segments ofsamples for signal S_(B) starting at sample start time T_(B). Arectifier 330 feeds the magnitude of the integrated segment of the S_(B)signal into adder 332. The output of adder 332 is a power signal 320that is fed back to the synchronizer 312. The IBS packet demodulator 322(FIG. 19) also includes a comparator 334 that generates either a binary1 value or a binary 0 value according to the magnitudes of the S_(A) andS_(B) signals.

To explain further, FIG. 21 shows a representation of the signals S_(A)and S_(B) that are output from the matched filter bank 310. A number ofsamples 336 of the S_(A) or S_(B) signal represent the bit duration T ofone IBS tone. In the example shown in FIG. 21, five samples are takenfor each bit duration T. The sample start time T_(B) is shifted onesample for each integration. A starting sample for the first integrationstarts at sample start time T_(b1). As seen in FIG. 21, the sample starttime Tb1 is not aligned with the S_(A) signal representing a binary “1”value or the S_(B) signal representing a binary “0” value. The syncdemodulator 314 in FIG. 20 generates a power output value of 0.0 forTb1.

When sample start time T_(B2) is used, the demodulator 314 generates anoutput value of −2.0. The sample start time T_(B3) represents the samplewith the best synchronization with the beginning of the “0” tone insignal S_(B). At synchronization start time TB3 the output power is −3.As the sample start times T_(B4) and T_(B5) move further away from thebest synchronization position, the magnitude of the output powerdecreases. FIG. 22 shows the magnitude of the power distribution for thedifferent sample start times. The maximum power magnitude is identifiedat sample start time T_(B3). Thus, the optimal sample start time T_(b3)is used by the IBS synchronizer 312 (FIG. 19).

Referring to FIGS. 20 and 21, a first sampling segment 338 starting atsample time T_(b3) generates an output value from adder 332 in FIG. 20of −3. The comparator 334 in FIG. 20 generates a binary “0” value forany adder value less than zero. The output of adder 332 for a secondsegment of sample values 340 generates an output value of +3. Becausethe output value for the second sample segment is greater than 0,comparator 334 generates a binary “1” value. The IBS packet demodulator322 (FIG. 19) continues to decode the tones in the S_(A) and S_(B)signals for the remainder of the IBS bit stream.

FIG. 23 shows a variation of the synchronization scheme described inFIGS. 19-22. The IBS tones are detected in block 341. The IBS tones areshifted to baseband by the multipliers 342 for both the audio tonefrequency f_(A) representing a binary bit “1” value and for the audiotone f_(B) representing a binary bit “0”. The baseband shift is done foreach individual sample T(x) of the f_(A) and f_(B) signals

Instead of summing an entire baud of samples, a running sum of thelatest baud value is taken using the new sample T(x) in block 344. Forexample, with a sample rate of 20 samples per bit, the 21^(st) sampleT(N+1) is deleted from the running sum and the next sample T(x) is addedto the running sum. The magnitude of the two running sums for tone A andtone B are each taken in blocks 345 and compared by comparator 346. Abinary “1” or binary “0” value is output from comparator 346 dependingupon which of the A tone or B tone samples has the largest magnitudevalue. The binary bit values output from comparator 346 are correlatedwith the known sync pattern in the correlation block 347. The selectedsample start time *T_(B) is identified as the last sample that generatesthe largest correlation value with the synchronization pattern. Theremaining bits in the IBS packet are then demodulated according to theselected sample start time *T_(B).

Multichannel Inband Signaling Modem

FIG. 24 shows the encoder portion 350 of a Multichannel Inband Signaling(MIBS) modem. A data source 351 generates a binary bitstream. The MIBSencoder 350 generates multiple inband signaling channels within the samevoice channel. A data buffer 352 stores the binary bit stream from thedata source 351. A packet assembler 353 assembles the bits in buffer 352into a packet payload and adds a preamble and postamble to the packetpayload to form IBS packets as described above in FIG. 4.

The encoder 350 includes two modulators 356 and 362 that each generatedifferent audio tones that represent the bits in the IBS packets.Modulator 356 modulates binary “1” values using an f1 frequency 360 andmodulates binary “0” values using an f2 frequency 358. Modulator 362modulates other bits in the IBS packets having binary “1” values usingan f3 frequency 364 and modulates binary “0” values using an f4frequency 366. The f1 and f2 tones output from modulator 356 arereferred to as a first Inband Signaling channel and the f3 and f4 tonesoutput from modulator 362 are referred to as a second IBS channel. Thetones output from the two modulators 356 and 362 are combined togetherby an adder 368 and then output to the D/A converter 370 and other cellphone circuitry 14 (FIG. 2). The cell phone circuitry 14 encodes andtransmits the tones in the two IBS channels over an audio channel of thecellular telephone network.

Each of the individual modulators 356 and 366 are similar in operationto the IBS modulator 64 shown in FIG. 4. Any number of IBS channels canbe generated in the IBS modem 24. For example, a third IBS channel couldbe provided by adding a third IBS modulator that modulates bits for athird portion of the IBS packets into tones using frequencies f5 and f6.The output of the third IBS modulator would be fed into the adder 368.However, for simplicity, only a two channel IBS modem with twocorresponding IBS modulators 356 and 362 are shown in FIG. 24.

An IBS channel controller 354 controls how the multiple IBS channels areutilized by the transmitting and receiving IBS modems. For example, afirst IBS channel may only be used by a first IBS modem for transmittingIBS packets and a second IBS channel may only be used by that first IBSmodem for receiving IBS packets. A second IBS modem on the opposite endof the transmission then uses the second IBS channel for transmissionand uses the first IBS channel for reception. The IBS channel controller354 adds control bits into the IBS packets that negotiate use of themultiple IBS channels between the two communicating IBS modems. Thedifferent configurations for the IBS modems are described in furtherdetail below in FIGS. 26 and 27. The controller 354 also controls whatportions of the IBS packets are modulated by modulators 356 and 362. Forexample, the modulators may modulate every other IBS packet or eachmodulator may modulate different portions of the same IBS packets.

FIG. 25 shows the decoder 375 of the MIBS modem. The audio tones fromthe audio channel are decoded by receiving circuitry 372 and fed into anA/D converter 374. A first filter 376 filters signals outside afrequency range of the two tones in the first IBS channel and a secondfilter 378 filters signals outside the frequency ranges of the two tonesin the second IBS channel. The frequency range of filter 376 is fromf1−Δf to f2+Δf and the frequency range of filter 378 is from f3−Δf tof4+Δf. The filters 376 and 378 are shown before the decoders 380 and382, respectfully. However, the filters 376 and 378 can be implementedin the same DSP anywhere in the decoding process.

A first IBS channel decoder 380 detects and demodulates the two tones inthe first IBS channel into binary bit values and a second IBS channeldecoder 382 detects and demodulates the two tones in the second IBSchannel into binary bit values. The decoders 380 and 382 detect,synchronize, and demodulate the IBS tones in the same manner aspreviously described for decoder 98 in FIG. 9 or decoder 300 in FIG. 19.A packet assembler 386 assembles the bits output from the two decoders380 and 382 into IBS packets that are then output to a data buffer 388.

The IBS channel controller 384 in the receiving IBS modem synchronizesthe two decoders 380 and 382 and determines which decoders demodulatewhat portions or which IBS packets. The controller 384 also conducts acommunication protocol with the transmitting IBS modem that negotiateswhich IBS modem is transmitting and which IBS modem is receiving IBSpackets over which IBS channels.

The filter 376 and decoder 380 for the first IBS channel and the filter378 and decoder 382 for the second IBS channel can be implemented insoftware in the same DSP. Alternatively, one DSP can be used for eachindividual channel encoder and decoder in each MIBS modem.

It is preferred in the “MIBS” modem for frequencies f1 & f2 to be farapart from frequencies f2 and f3. One advantage of MIBS is interferencemitigation and the ability to adapt to variations in cell phoneperformance across manufacturers by dynamically changing frequencieswhen performance is bad. A robust low baud rate control signal can besent to choose a new frequency when one modem is detecting errors.

FIG. 26 shows one possible configuration for two Multichannel InbandSignaling (MIBS) modems 390 and 396. The two IBS channels 398 and 400are transmitted from MIBS modem 390 over the voice channel of a wirelesscommunications network and then possibly through a landline telephonenetwork to the MIBS modem 396. The two MIBS modems shown in FIG. 26operate in a half duplex mode where one of the IBS modems transmits IBSpackets over both the first IBS channel 398 and the second IBS channel400 at the same time.

After the first IBS modem 390 has completed a transmission 392 of IBSpackets over the two IBS channels, the second IBS modem 396 is allowedto begin a transmission 394 back to modem 390 over the two IBS channels398 and 400. The MIBS modem 390 sends information in one of the IBSpackets indicating to the MIBS modem 396 that the transmission 392 iscompleted.

FIG. 27 shows an alternative configuration where the first IBS channel398 is dedicated to transmitting IBS packets from MIBS modem 390 and thesecond IBS channel 400 is dedicated to transmitting packets from MIBSmodem 396. Thus, both MIBS modem 390 and 396 can transmit and receivepackets at the same time. This full duplex configuration can providefaster communications for certain types of IBS transmissions.

The MIBS modem 390 may transmit different potions of the same IBSpackets over the two IBS channels 398 and 400 or may alternatetransmission of different IBS packets over the two IBS channels. Inother configurations, one IBS channel may be used for transmitting IBSpackets and the second IBS channel may be used exclusively for signalingand protocol communications between the two MIBS modems. In otheralternative configurations, portions of bits from the same IBS packetsare interleaved in the two IBS channels or the same IBS packets aretransmitted over both IBS channels for redundancy. The information inthe two IBS channels can be reconfigured according to the applicationassociated with IBS packet data.

A request to reconfigure the IBS channels can be encoded into the IBSpacket header. For example, the IBS channel controller 354 (FIG. 24) inMIBS modem 390 may send an IBS packet to MIBS modem 396 that contains areconfiguration request in the IBS packet preamble 73 (FIG. 5). Thereconfiguration request from modem 390 may request both the first IBSchannel 398 and the second IBS channel 400 and then request allocationof a third IBS channel 401, with a slower baud rate, to MIBS modem 396for transmitting acknowledge messages back to modem 390. MIBS modem 390then waits for an acknowledge of the configuration request from modem396.

The IBS channel controller 384 (FIG. 25) in MIBS modem 396 reads thereconfiguration request in the IBS packet preamble. The controller 384then outputs an acknowledge back through the encoder of MIBS modem 396.The encoder formats the acknowledge into the preamble of a reply IBSpacket that is then modulated and transmitted back to MIBS modem 390over one or more of the currently allocated IBS channels. The controllerin the modem 396 then reconfigures the encoder to receive IBS packetsover the first and second IBS channels 398 and 400 and transmit packetsover the third low baud rate channel 401.

When the acknowledge from modem 396 is received at modem 390, thecontroller directs the encoder and the decoder in the modem 390 totransmit over the first and second IBS channels and receive from the lowbaud rate third channel. The two modems 390 and 396 then transmits andreceive IBS packets according to the new channel configuration.

Multicarrier Inband Signaling Modem

FIG. 28 shows a Multicarrier Inband Signaling modem according to oneembodiment. The multichannel IBS modem described in FIGS. 24-27generates two different audio tones, one tone representing a binary “1”value and a second tone representing a binary “0” value. The two tonesare generated in a sequential tone stream over time to represent abinary bit stream.

The multicarrier IBS modem in FIG. 28 generates multiple audio tones atthe same time, where each tone represents a different bit location in afour bit portion of the IBS packet. The particular audio tone associatedwith one of the four bit locations represents a binary “1” value (oralternatively a binary “0” value). If the audio tone is not generatedfor a particular bit time (baud), the IBS decoder assumes the binary bitvalue associated with that bit location is “0”.

Referring to FIG. 28, a stream of bits are input to data buffer 402 fortransmission over the audio channel of a wireless communicationsnetwork. A packet formatter 404 formats those bits into an IBS packet. Afirst portion of one of the IBS packets contains the bits “1010”. Thepacket formatter 404 outputs each one of the four bits into a differentone of the four modulators 406, 408, 410 and 412. The first bit “1” ofthe four bit sequence is referred to as bit B1, the second bit “0” isreferred to as bit B2, the third bit “1” of the four bit sequence isreferred to as bit B3, and the fourth bit “0” is referred to as bit B4.

Modulator 406 receives bit B1, modulator 408 receives bit B2, modulator410 receives bit B3, and modulator 412 receives bit B4. Because bit B1is a binary “1” value, modulator 406 generates a tone at frequency f1during the first baud period. The modulator 408 does not generate an f2tone for the first baud period because the B2 bit is a binary “0” value.Accordingly, modulator 410 generates a f3 tone during the first baudperiod and modulator 412 does not generate a f4 tone during the firstbaud period. The modulators work in essentially the same manner as theIBS modulator 64 in FIG. 4 except that a frequency tone is generated forthe binary “1” values and no tone is generated for the binary “0” value.

The f1 and f3 tones are combined together by summer 414. A digital toanalog converter 416 converts the digital signal into an analog signalthat is fed into cell phone transmit circuitry 418. The transmitcircuitry 418 transmits the audio tones over the voice channel of thecellular telephone network.

FIG. 29 shows the decoder for the multicarrier IBS modem. Receivecircuitry 420 receives the IBS tones from the voice channel of thecellular communications network. An A/D converter 422 converts the audiotones into a digital signal. Four bandpass filters 424, 426, 428 and 430each are centered about the frequency for the tones f1, f2, f3, and f3,respectively. The tone representing the binary bit B1 passes throughbandpass filter 424 while other tones, such as tone f3, are filtered bythe bandpass filter f1. Decoder 432 identifies the tone f1 in a mannersimilar to the IBS decoder described in FIGS. 11-13, only for a singletone. Because the f1 tone was detected by decoder 432, a binary “1”value is generated representing bit B1 in the four bit sequence.

Because no f2 tone will be detected by decoder 434, a binary “0” valueis generated for bit B2 in the four bit sequence. Decoder 436 detects anf3 tone and accordingly generates a binary “1” value for bit B3. Decoder438 generates a binary “0” value for bit B4 because no f4 tone wasgenerated by the multicarrier encoder. A packet assembler 440 receivesthe four bits B1-B4 and places them into the appropriate IBS packetlocation in the data buffer 442.

The terms and descriptions used herein are set forth by way ofillustration only and are not meant as limitations. Those skilled in theart will recognize that many variations can be made to the details ofthe above-described embodiments without departing from the underlyingprinciples of the invention. The scope of the invention should thereforebe determined only by the following claims (and their equivalents) inwhich all terms are to be understood in their broadest reasonable senseunless otherwise indicated.

1. A system for receiving a data payload over a voice channel of atelecommunications network, comprising: a vocoder component for decodinga digital data stream received from the voice channel of thetelecommunications network into audio tones, the audio tonesrepresenting voice data and the data payload; a frequency conversioncomponent for converting the audio tones into at least one data packetincluding a preamble and the data payload; a packet disassemblingcomponent for extracting the data payload from the at least one datapacket; and a storage component for storing the data payload; whereinthe frequency conversion component includes: a first bandpass filter forattenuating frequencies outside of a range of frequencies, the range offrequencies including audio tones that represent a binary “0” bit and abinary “1” bit; a second bandpass filter for attenuating frequenciesinside of the range of frequencies; a SNR component coupled to an outputof the first bandpass filter and an output of the second bandpassfilter, the SNR component determining a signal-to-noise ratio betweenthe output of the first bandpass filter and the output of the secondbandpass filter; and a comparator coupled to the SNR component, thecomparator identifying audio tones representing the data payload whenthe signal-to-noise ratio exceeds a threshold.
 2. The system of claim 1wherein the range of frequencies is substantially within a range of 400Hertz to 700 Hertz.
 3. A system for receiving a data payload over avoice channel of a telecommunications network, comprising: a vocodercomponent for decoding a digital data stream received from the voicechannel of the telecommunications network into audio tones, the audiotones representing voice data and the data payload; a frequencyconversion component for converting the audio tones into at least onedata packet including a preamble and the data payload; a packetdisassembling component for extracting the data payload from the atleast one data packet; and a storage component for storing the datapayload; wherein the frequency conversion component includes: a samplerfor extracting a plurality of samples associated with a single bit fromthe audio tones; a first discrete Fourier transform for analyzingfrequencies contained in the plurality of samples, the first discreteFourier transform generating a correlation value when the plurality ofsamples contain a first frequency representing a binary “0” bit; asecond discrete Fourier transform for analyzing frequencies contained inthe plurality of samples, the second discrete Fourier transformgenerating a correlation value when the plurality of samples contain asecond frequency representing a binary “1” bit; and a bit selectioncomponent for comparing the correlation value generated by the firstdiscrete Fourier transform and the correlation value generated by thesecond discrete Fourier transform, the bit selection component selectinga binary “0” if the correlation value generated by the first discreteFourier transform is greater than the correlation value generated by thesecond discrete Fourier transform and a binary “1” if correlation valuegenerated by the second discrete Fourier transform is greater than thecorrelation value generated by the first discrete Fourier transform. 4.The system of claim 3 wherein the first frequency is approximately 500Hertz and the second frequency is approximately 600 Hertz.